class Student {    fullName: string;    constructor(public firstName, public middleInitial, public lastName) {        this.fullName = firstName + " " + middleInitial + " " + lastName;    }}interface Person {    firstName: string;    lastName: string;}function greeter(person : Student) {    return "Hello, " + person.firstName + " " + person.lastName;}let user = new Student("Jane", "M.", "User");document.body.innerHTML = user.middleInitial;